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Oxyrane U.K. Ltd. and BioMarin Pharmaceutical Inc. have
separately reported on their next-generation enzyme replacement therapies for
Pompe's disease. Both molecules cleared glycogen from
mouse muscle better than the marketed drug Myozyme
from Sanofi.1,2
BioMarin has moved its therapy into a Phase I/II trial, whereas Oxyrane is
carrying out IND-enabling animal toxicology studies.

Pompe's
disease is an inherited disorder of glycogen metabolism caused by an absence of
or deficiency in the lysosomal enzyme acid α-glucosidase (GAA). The resulting accumulation of
glycogen in cardiac and skeletal muscle leads to severe and progressive muscle
weakness, cardiomyopathy and respiratory failure.

The
problem is that skeletal muscle cells are less accessible to systemic enzyme
replacement therapy than cells targeted in other lysosomal storage diseases.
Indeed, the drugs are typically delivered at doses 20-30 times higher than
other enzyme replacement therapies.3 These high doses can lead to
long infusion times and adverse reactions, including fever, tachycardia,
cyanosis and hypotension.4

Thus,
Oxyrane and BioMarin have been modifying GAA to improve its uptake into
skeletal muscle and make possible the use of lower doses.

The
Oxyrane group hypothesized that enhancing levels of the carbohydrate mannose-6-phosphate (M-6-P) on the surface of GAA would
increase its uptake by muscle cells. The binding of M-6-P to IGF2R is known to
mediate delivery of proteins to the lysosome.5-7

Oxyrane
used the yeasts Yarrowia lipolytica and Pichia pastoris to
produce modified GAA. In prior work, Oxyrane researchers and colleagues had
engineered those yeast to yield much higher levels of carbohydrate
modifications than the mammalian cell lines used to produce Myozyme and
Lumizyme.8,9

In the new paper, the group showed that the resulting
carbohydrate-enriched GAA was purified from the yeast and treated with two
processing enzymes to generate the final M-6-P-modified GAA,
which had more than 15-fold higher M-6-P content than unmodified GAA.

Importantly,
those higher M-6-P levels led to greater uptake of GAA by cultured fibroblasts
from patients with Pompe's disease than uptake of unmodified GAA.

Finally,
in a mouse model of Pompe's disease, the M-6-P-enhanced GAA cleared more
glycogen from heart and thigh muscle than unmodified GAA.

The
BioMarin group expected that linking a high-affinity endogenous ligand of IGF2R
to GAA would increase uptake of the enzyme into muscle cells. Thus, they tagged
GAA with a portion of insulin-like
growth factor-2 (IGF-2), a ligand previously shown by some
of the same BioMarin researchers to promote uptake of the lysosomal enzyme b-glucuronidase into fibroblasts.10

The
tagged GAA, dubbed BMN-701 (IGF-2-GAA) was produced in
mammalian cells, purified and shown to have the same enzymatic activity as
untagged GAA. Moreover, BMN-701 showed greater uptake by rodent fibroblasts
than Myozyme.

In
mice with Pompe's disease, BMN-701 increased clearance of glycogen from the
heart, diaphragm and multiple skeletal muscles compared with Myozyme.

The
Oxyrane and BioMarin findings were published in Nature Biotechnology and
The Journal of Biological Chemistry, respectively.

"We
think it is possible that BMN-701 could achieve the same clinical benefit in
patients as Myozyme but at lower doses. However, there is also the possibility,
which is our current hope, that BMN-701 will show greater clinical benefit than
the marketed drug at comparable higher doses," he said.

A
potential advantage of BMN-701 over carbohydrate-modified GAA, said LeBowitz,
is that "the IGF-2 tagging approach doesn't rely on post-translational
carbohydrate modifications, which can be difficult to control in large-scale
bioreactors and could lead to regulatory challenges."

Indeed,
differences in carbohydrate modifications of Myozyme produced in a 4,000-liter
bioreactor versus enzyme produced in the original 160-liter bioreactor led the
FDA to require a separate approval for the drug at the higher scale. The resulting
product is marketed as Lumizyme.11

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